Dominance
Lex had been homeschooled a lot, so he did not know what a traditional P.E. teacher was like. The only thing he had to compare it with was when his dad would put on a tracksuit, grab a whistle and make him and his sisters do odd, random exercises.
Sometimes they would run laps around a random park and other times they'd go swimming. Sometimes, his parents would get creative after watching a martial arts movie, like The Karate Kid or something, and then make them do the same things as in the movie.
All in all, it was not too bad except for the fact that they would not be allowed to stop till they were thoroughly exhausted and drained. In hindsight, maybe it was just a way for parents to exhaust extremely energetic kids to get some rest themselves. If his parents were normal, that would have made sense.